Introduction

In this blog post, we will explore how to solve the LeetCode problem "744" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

You are given an array of characters letters that is sorted in non-decreasing order, and a character target. There are at least two different characters in letters. Return the smallest character in letters that is lexicographically greater than target. If such a character does not exist, return the first character in letters. Example 1: Input: letters = ["c","f","j"], target = "a" Output: "c" Explanation: The smallest character that is lexicographically greater than 'a' in letters is 'c'. Example 2: Input: letters = ["c","f","j"], target = "c" Output: "f" Explanation: The smallest character that is lexicographically greater than 'c' in letters is 'f'. Example 3: Input: letters = ["x","x","y","y"], target = "z" Output: "x" Explanation: There are no characters in letters that is lexicographically greater than 'z' so we return letters[0]. Constraints: 2 <= letters.length <= 104 letters[i] is a lowercase English letter. letters is sorted in non-decreasing order. letters contains at least two different characters. target is a lowercase English letter.

Explanation

Here's the breakdown of the solution:

• Binary Search: Leverage the sorted nature of the letters array to efficiently find the target's successor using binary search.

• Wrap-around: Handle the case where the target is larger than all characters in letters by returning the first element.

• Time Complexity: O(log n), where n is the length of the letters array. Space Complexity: O(1).

Code

    def nextGreatestLetter(letters, target):
    """
    Finds the smallest character in letters that is lexicographically greater than target.

    Args:
        letters: A sorted array of characters.
        target: A character.

    Returns:
        The smallest character in letters that is lexicographically greater than target.
        If such a character does not exist, return the first character in letters.
    """
    left = 0
    right = len(letters) - 1

    while left <= right:
        mid = left + (right - left) // 2
        if letters[mid] > target:
            right = mid - 1
        else:
            left = mid + 1

    return letters[left % len(letters)]